conclusive evidence or proof When the law says that a particular kind of evidence would be conclusive as to the existence of a particular fact, it implies that, that fact, can be proved either by that evidence or some other evidence which the court permits or requires to be adduced. In the former, the court has no option, but in the latter, the court is to consider whether the evidence adduced is sufficient. The aim of the expressions conclusive evidence and conclusive proof is to give finality to the establishment of the existence of a fact from the proof of another